Experiments aimed at the elucidation of the chemistry and mechanism of BU-nucleic acid protein photocrosslinking will be performed. The importance of a proposed bromouracil hydrogen atom abstraction type mechanism will be assessed, the intermediacy of a bromouracil triplet state or triplet states will be established, and the intersystem crossing efficiency of bromouracil will be measured. Photoreactivity of bromouracil with N-acyl amino acid amines as models for simple peptides will be determined in fluid and frozen aqueous medium. Frozen medium will be used to enhance the probability for bromouracil peptide crosslinking. N-acyl amino acid amides and dipeptide amides chemically linked to 5-bromouracil and 1-methyl-5-bromouracil at the 6-position will be synthesized and investigated for photochemical reactivity as a model for the photochemistry of a nucleic acid protein complex. The results of this investigation will lead to the development of the BU-nucleic acid protein photocrosslinking technique as a powerful method for the study of important protein nucleic acid interactions.